Voltage and current regulated power supply circuit for gaseous discharge lamp

ABSTRACT

A voltage and current regulated circuit operative to supply sinusoidal high-frequency (28 kilohertz) electrical power which meets both the starting and running requirements of a gaseous discharge lamp without mechanical switching means or saturable reactors.

United States atet Quinn Sept. 5, 1972 [54] VOLTAGE AND CURRENT REGULATED POWER SUPPLY CIRCUIT FOR GASEOUS DISCHARGE LAMP Inventor: Halsey P. Quinn, Morris Plains,

[73] Assignee: Wagner Electric Corporation Filed: Dec. 30, 1970 Appl. No.: 102,610

US. Cl. ..323/20, 315/276, 315/308, 323/45, 323/62 Int. Cl ..G05f 1/30 Field of Search ..315/254, 257, 276, 278, 306, 315/308, DIG. 2, DIG. 5, DIG. 7; 323/6, 20,

Primary Examiner-A. D. Pellinen Attorney-Eyre, Mann & Lucas [57] ABSTRACT A voltage and current regulated circuit operative to supply sinusoidal high-frequency (28 kilohertz) electrical power which meets both the starting and running requirements of a gaseous discharge lamp without mechanical switching means or saturable 22 T, 44, 45, 62; 321/16, 18, 19 reactors.

11 Claims, 3 Drawing Figures M an! a '1 M2 5/4 15b V 2 400d M USC/LLATUR I m4 Jfl9 /2 1 1 f 6/2 I W2 my 9 6 $7 2.. '1' 706 My \ML E ;.f i J 1 20? 204 I \g 4 9] E i 972 9/4 i .916 9/2/- gw i L: M J/d SUPPLY CIRCUIT FOR GASEOUS DISCHARGE LAMP BRIEF SUMMARY OF THE INVENTION The present invention relates to a power supply circuit, operative to generate and regulate both sinusoidal high-frequency voltage and current outputs for a variable-impedance load having widely-variable voltage and current requirements, e.g., a gaseous discharge lamp. Such a load presents a unique problem because it initially requires a very high, regulated starting voltage and then, after the gaseous discharge has been initiated by the vflow of current through the lamp, a constant lamp current at a low voltage is required. Earlier supply circuits have used a high-voltage starting circuit which, when the lamp passes current, is switched off by a relay which simultaneously connects the lamp to a low-voltage constant current supply circuit. Saturable reactors have been commonly employed in such prior art circuits.

The present invention is embodied in a single supply circuit which does not utilize saturable reactors and which has two modes of operation, one for starting and one for running the lamp. The output voltage is regulated when the supply circuit is in the starting mode, and the output current is regulated when the supply circuit is in the running mode. A resonant circuit builds up a controlled high voltage only during the starting mode.

I To supply constant high current at a lower voltage in the running mode, current regulation is effected by supplying high-frequency current pulses of constant amplitude and variable width to the input of a power circuit. The width of the pulses is controlled by a variable bias voltage derived .from the output of the supply circuit combined with a series of saw-tooth pulses in a summation circuit. A significant feature of this invention is the generation of a saw-tooth wave in synchronization with an oscillator by charging a capacitor through a first current path during one time interval and discharging that capacitor through the oscillator during a second time interval corresponding to the interpulse null of the oscillator.

' BRIEF DESCRIPTION OF THE DRAWINGS Y to generate high-frequency periodic rectangular pulses.

DETAILED DESCRIPTION OF THE INVENTION Referring now specifically to FIG. 1, the circuit shown therein is operable with a standard alternating current power source (117 volts RMS, 60 hertz) connected between input terminals 002 and 004. A switch 006 connected to the high input terminal 002 enables control of the application of power to transformer 100,

which energizes the filaments of lamp 200, and to the AC/DC conversion circuit 300, the output of which is fed to high frequency oscillator 400 via switch 008 and resistance 010, to variable-width pulse generator 500, and to power circuit 600. The high-frequency sinusoidal output voltage and current are monitored by voltage and current sensing circuits 800 and 900, respectively, the outputs of which are fed to bias circuit 1000. The output of the bias circuit 1000 is fed to the variable-width pulse generator 500 to cause variations in the width of the high-frequency, constant-amplitude pulses which comprise the input to power circuit 600.

The AC/DC conversion circuit 300 includes a diode bridge full-wave rectifier circuit comprising diodes 5 302, 304, 306 and 308, a pair of choke coils 310 and 312 which are preferably inductively coupled by a common core 314 to act as a low-pass filter, and a capacitor'3l6 to eliminate substantially all of the AC ripple in the DC output. An output voltage of approximately bolts DC is generated across capacitor 316 and is applied through switch 008 and resistance 010 to high-frequency oscillator 400, which is illustrated in detail in FIG. 3 and described in subsequent paragraphs.

The DC power output of AC/DC conversion circuit 300 is applied to the variable-width pulse generator 500 through the current-limiting resistance 516, which is efiectively in series with zener diode 524 between the output terminals of the AC/DC conversion circuit 300. Thus, a constant DC voltage of approximately 5 volts DC is applied to the variable-width pulse generator 500, which comprises a charging circuit formed by resistance 502 and'capacitance 520, their junction being connected via resistance 504 to the base of transistor 526. A discharge circuit for capacitance 520 is formed by diode 522 and resistance 506 connected in series between the aforementioned junction and the output terminal of high-frequency oscillator 400. During each of the positive high-frequency rectangular pulses which comprise the output of oscillator 400, the discharge path is effectively blocked because the cathode of diode 522 is placed at a positive potential. Thus, during each pulse, charging current flows through resistances 516 and 502 to capacitance 520. Between pulses, capacitance 520 discharges through diode 522, resistance 506, and the high-frequency oscillator 400. In this manner, saw-tooth pulses having the same frequency as the output of oscillator 400 appear at the junction of resistance 502 and capacitance 520, and are applied through resistance 504 to the base of transistor 526. These saw-tooth pulses, along with the variable negative DC bias derived from the bias circuit 1000 and applied to the base of transistor 526, are amplified by the two-stage DC amplifier formed by transistor 526, resistance 508, transistor 528 and resistance 512. The combined and amplified saw-tooth pulses and variable DC bias comprise one input to the NAND gate 532,

and the positive high-frequency rectangular output pulses of oscillator 400 comprise the second input to the NAND gate 532. Only when both of these positive input signals are above the threshold voltage of NAND gate 532 is a negative output signal generated. Since the period of time during which the first input signal is above that threshold varies according to the variable DC component of the first input signal, the output pulses of NAND gate 532 will vary accordingly. The variable-width, constant-amplitude, negative pulses which capacitance 518 to the base of normally conductive amplifier transistor 530, which is resultantly pulsed non-conductive to provide variable-width, positive input voltage pulses to the low terminal of winding 614 in power circuit 600.

The primary winding 614 of transformer 610 is connected in series with resistance 604 between the positive terminal of AC/DC conversion circuit 300 and the collector of transistor 530. Thus, with each variable width, positive voltage pulse applied to the low terminal of primary winding 614, the flow of current through that winding is interrupted and a pulse of corresponding width is induced in the secondary winding 612 and applied across the base-emitter junction of power transistor 608. Consequently, transistor 608 is rendered conductive for variable periods of time corresponding to the width of each input pulse thus generated across secondary winding 612 of transformer 610. During these periods of conductivity of transistor 608, current flows from the positive terminal of AC/DC conversion circuit 300, through input winding segment 618 of autotransformer 616, and through the collectoremitter junction of transistor 608 to ground. Thus, high-frequency power pulses are generated across the output winding 618 620 of autotransformer 616. These periodic power pulses, whose frequency corresponds to that of high-frequency oscillator 400, are applied to the resonant circuit 700.

The resonant circuit 700 comprises first capacitance 702 connected across the output terminals of the autotransformer 616, a second capacitance 704 of approximately one-third the magnitude of first capacitance 702, and an inductance 706 connected between the low terminals of capacitances 702 and 704, whose high terminals are both connected to the positive output terminal of AC/DC conversion circuit 300, and to the lamp filament 204 by a center-tap connection to secondary winding 104 of transformer 100. Also, the low side of capacitance 704 is connected through the primary winding 916 of transformer 914 and through a center-tap connection of secondary winding 106 of transformer 100 to filament 202 of lamp 200. The high-frequency power pulses appearing across the output terminals of autotransformer 616 are injected into the series resonant circuit 700 and cause that circuit to oscillate at the second harmonic of the frequency of the power pulses when the impedance of lamp 200 is high, i.e., when the lamp has not been started. Conse-quently, the voltage across the smaller capacitance 704 becomes very high and effects start-up of the lamp 200. The voltage thus developed across the relatively high impedance of capacitance 704 has the frequency of the second harmonic of the high frequency power pulses injected into resonant circuit 700, i.e.,

slow-down action on the charging current to capacitance 702, which in turn loads the autotransformer 616 so as to prevent large inductive kicks on power transistor 608. By judicious selection of the characteristics of autotransformer 616, dissipation in transistor 608 can be minimized.

The voltage applied to the load across the center-tap connections from the resonant circuit 700 to the secondary windings 104 and 106 of transformer. is monitored by the voltage sensing circuit 800, which is connected to the center-tap connection to the secondary winding 106. From this point, a capacitance 804 is connected to the junction of a pair of series-connected diodes 808 and 810, which are paralleled by a capacitance 806 and by a resistance 802, the output signal being derived from the latter by an adjustable tap connected through isolating diode 812 to bias circuit 1000. Diode 812 blocks the output current signal from current sensing circuit 900.

The current sensing circuit 900 is of similar construction, but includes a transformer 914 having fixed and variable resistances 902 and 904, respectively, connected in series across its secondary winding 918, withthe primary winding 916 being connected in series with inductance 706 of resonant circuit 700 and the center tap connection to the secondary winding 106 of transformer 100. A capacitance 906 is connected from a junction of secondary winding 918 and resistance 902 to the junction of two series-connected diodes 910 and 912, which are paralleled by a capacitance 908. The output of this circuit is derived from the junction of capacitance 908 and the anode of diode 912, and is applied to bias circuit 1000 along the same conductor as the output of current sensing circuit 800.

Bias circuit 1000 comprises resistances 1002 and 1004 connected in series between the base of transistor 526 and the outputs of voltage and current sensing circuits 800 and 900, and a resistance 1006 connected from the high side of voltage-regulating zener diode 524 to the junction of resistances 1002 and 1004. These three interrelated circuits 800, 900 and 1000 form a feed-back loop from the 'output of the supply circuit to the first stage of the two-stage DC amplifier of the variable-width pulse generator 500. In the voltage sensing circuit 800, the high-frequency alternating voltage impressed across the lamp filaments 202 and 204 is passed through capacitance 804, rectified by the diodes 808 and 810, and filtered by capacitance .806. The voltage across capacitance 806 is impressed across resistance 802, from which a negative signal is picked off through a tap and applied through isolating diode 812 to the bias circuit. This signal is added through resistance 1004 to the steady positive bias voltage generated across resistances 1006 and 1002 of the bias circuit 1000. Thus, if the voltage across the lamp 200 is too large, the negative DC voltage applied by voltage sensing circuit 800 will alter the bias at the base of transistor 526 by making it less positive. Consequently,

the DC component of the signal applied as the first input to the NAND gate 532 will be lowered so as to cause a decrease in the width of the output pulses of the pulse generator 500. On the other hand, if the voltage across the lamp 200 is too low, the opposite variation is made upon the bias voltage at the base of transistor 528, with the opposite effect of increased pulse width.

The current sensing circuit 900 performs a similar function by generating a voltage across the two seriesconnected resistances 902 and 904 across the secondary winding 918 of transformer 914, applying this voltage through capacitance 906 to rectifying diodes 910 and 912 which cause capacitance 908 to become negatively charged with respect to ground. Variations in the level of negative charge will cause variations in the net bias voltage at the base of transistor 526 and consequently in the width of the output pulses of pulse generator 500 in the same manner as described above.

' Referring now specifically to FIG. 2(a), these rectangular pulses represent the output of oscillator 400. FIG. 2(b) illustrates the saw-tooth pulses generated at the base of transistor 526, with the dotted line representing the net negative voltage fed to bias circuit 1000 by the voltage and current sensing circuits 800 and 900, respectively. As can be seen in FIG. 2(c), the width of the output pulses of the two-stage DC amplifier appearing at the collector of transistor 528 are narrowed as a result of the increasingly negative DC bias. By way of contrast, FIG. 2(d) illustrates the voltage at the base of the first-stage transistor 526 when the negative voltage produced by the voltage and current sensing circuits is relatively low, resulting in wider pulses appearing at the collector of transistor 528 as shown in FIG. 2(e). FIG. 2(f) illustrates the wave form of the bias voltage appearing at the base of transistor 530 during circuit operation. Absent any output from NAND circuit 532, the base is slightly positive. When a negative pulse is produced by NAND circuit 532 in response to coincident above-threshold input signals to its first and second gates, this negative pulse is applied via capacitance 518 to the base of transistor 530 to render same negative, thereby cutting off the flow of current from the positive terminal of AC/DC conversion circuit 300 through resistance 604, through the primary winding 614 of transformer 610 and the parallel-connected resistance 602, and through the collector-emitter junction of transistor 530. Thus, a pulse is generated across secondary winding 612 of transformer 610 corresponding in duration to the period of nonconductivity of transistor 530. Power transistor 608 becomes conductive for a like period of time and causes the generation of a current pulse of equal duration in the input winding segment 618 of autotransformer 616. As may be seen in FIG. 2( g), the collector of transistor 530, which is normally at virtually ground potential when this transistor is conductive, becomes positive for periods corresponding directly to the duration of the negative pulses applied by NAND circuit 532 to the base of transistor 530.

Referring now specifically to FIG. 3, this is a schematic diagram of the oscillator circuit 400 shown in block form in FIG. 1. Although any oscillator which serves to generate high-frequency rectangular pulses and which affords. a low-impedance path to ground through its output terminal during interpulse nulls will serve, the oscillator circuit shown in FIG. 3 is preferred because of its efiiciency. This oscillator circuit comprises essentially a first-stage transistor switch having its output connected to the input of a second-stage transistor switch, with a resonant series circuit interconnecting the input of the first-stage switch and the output of the second-stage switch. The output of the first-stage switch is connected to the input of that switch via a feedback loop comprising resistance 419 to make the oscillator circuit more linear and to enable oscillation.

In the circuit which forms the preferred embodiment of the invention and which is shown in FIGS. 1 and 3.,

the values of the various circuit elements are as follows:

Resistances 010 SK ohms 012 470 ohms Capacitances 3.16 200 micmfarads 422 8.2 picofar ads 512 10K ohms 514 4.7K ohms 424 4.3 millihenries 706 .36 millihenry 516 2K ohms 602 l.5l( ohms Diodes 604 2K ohms 802 20K ohms 302- 902 33 ohms 904 1 ohms 3D6 Varo Part No. VS 447 1002 10K ohms 308- 1004 10K ohms 426 (IC) 1006 10K ohms 428 -(IC) 522 lN9l4 Transistors 524 lN522l 808 lN5059 430 (IC) 810 1N5059 432-(IC) 812- lN9l4 434-(IC) 910- 1N9l4 436-(IC) 912- 1N9l4 43s (IC) 440 (IC) Transformers 442 (IC) 4 Primary winding 102 526 2N5 l 83 I 1 M5 turns Secondary windings 528 2N5l83 104 and 106 47 turns 530 DTS411 610 Primary winding 614 5 turns Secondary winding 610 608 MJE34O I50 turns 616 Winding segment 618 84 turns Winding segment 620 NAND Gate l4 turns 914 Primary winding 616 s turns Secondary winding 918 532 integrated with ISO turns oscillator 400; SN74 00N The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiment thereof, will be readily apparent to those skilled in the art. It is the applicant's intention to cover all those changes and modifications which could be made to the embodiment of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

WHAT IS CLAIMED IS:

1. A voltage and current regulated power supply cir-,

pulses of variable width and substantially constant amplitude;

3. third circuit means which, when coupled to the variable-impedance load is operative in response to the output of said second circuit means to generate high frequency, high voltage output power when the load impedance is high, and to generate high frequency, low voltage output power when the load impedance is low; and

. fourth circuit means operative to provide a variable bias signal to said second circuit means to vary the width of the output pulses of said second circuit means in response to variations in the output voltage and current from their predetermined normal levels.

2. The power supply circuit according to claim 1 wherein said first circuit means comprises:

1. a diode bridge circuit having first and second input and output terminals;

2. first and second inductances each having first and second terminals, said first terminal of said first inductance being connected to said first output terminal of said diode bridge circuit, and said first terminal of said second inductance being connected to said second output terminal of said diode bridge circuit; and

3. a filtering capacitance connected between said second terminals of said first and second inductances.

3. The power supply circuit according to claim 2 wherein said first and second inductances are inductively coupled by a common magnetic core.

4. The power supply circuit according to claim 1 wherein said second circuit means comprises:

1. high frequency oscillator means operative to generate high-frequency rectangular pulses;

2. saw-tooth pulse generating means synchronized with said high-frequency oscillator means;

3. first amplification circuit means connected to said saw-tooth pulse generating circuit and operative to amplify the output of said saw-tooth pulse generating means and said variable bias signal;

4. threshold circuit means having a first input terminal connected to the output of said first amplification circuit means and a second input terminal connected to the output of said high-frequency oscillator means, and operative to generate output pulses of constant amplitude and of variable width corresponding to the period of time during which both of said input pulses exceed its threshold; and

5. second amplification circuit means operative to generate output pulses of predetermined polarity, constant amplitude, and variable width corresponding to the width of the output pulses of said threshold circuit means.

5. The power supply circuit according to claim 4 wherein said high-frequency oscillator means comprises:

1. a first-stage transistor switch including a feedback 2. a second-stage transistor switch; and

3. a series resonant circuit interconnecting the input of said first-stage transistor switch and the output of said second-stage transistor switch. I 6. The power supply circuit according to claim 5 wherein said high-frequency oscillator means is operative to close a dischar e curren at h for said saw-t oth pulse generating meafis through s d second transistor switch in the periods between adjacent high-frequency rectangular pulses.

7. The power supply circuit according to claim 4 wherein said threshold circuit means comprises a NAND gate. 7

8. The power supply circuit according to claim 4 wherein said second circuit means further comprises voltage regulation means.

9. The power supply circuit according to claim 8 wherein said saw-tooth pulse generating circuit comprises:

1. a capacitance and a charging resistance connected 3. a power transistor having its base and emitter connected across said secondary winding of said transformer, and having its collector connected through said second and first terminals of said autotransformer to said first circuit means; and

4. resonant circuit means connected between said first and thrid terminals of said autotransformer and operative to generate a high voltage by resonating at a first high frequency in response to input power pulses from said autotransformer when said load impedance is high, and by resonating at a second high frequency in response to input power pulses from said autotransformer when said load impedance is low.

11. The power supply circuit according to claim 1 wherein said fourth circuit means comprises:

1. voltage sensing circuit means operative to generate an output voltage deviating from a predetermined norm in response to variations in the output voltage of said power supply circuit from a predetermined value;

2. current sensing circuit means operative to generate an output current deviating from a predetermined norm in response to variations in the output current of said power supply circuit from a predetermined value, and

3. bias circuit means coupled to said voltage-and current-sensing circuit means and operative in response to the output voltage and current received therefrom to provide said variable bias signal to said second circuit means. 

1. A voltage and current regulated power supply circuit for a variable-impedance load, comprising:
 1. first circuit means operative to convert alternating current power to direct current power which is applied to the remainder of said power supply circuit;
 2. second circuit means operative in response to a variable bias signal to generate high-frequency pulses of variable width and substantially constant amplitude;
 3. third circuit means which, when coupled to the variableimpedance load is operative in response to the output of said second circuit means to generate high frequency, high voltage output power when the load impedance is high, and to generate high frequency, low voltage output power when the load impedance is low; and
 4. fourth circuit means operative to provide a variable bias signal to said second circuit means to vary the width of the output pulses of said second circuit means in response to variations in the output voltage and current from their predetermined normal levels.
 2. a diode and a discharging resistance connected in series between the junction of said capacitance and said charging resistance and the output terminal of said high-frequency oscillator.
 2. an autotransformer having first, second and third terminals;
 2. first and second inductances each having first and second terminals, said first terminal of said first inductance being connected to said first output terminal of said diode bridge circuit, and said first terminal of said second inductance being connected to said second output terminal of said diode bridge circuit; and
 2. a second-stage transistor switch; and
 2. current sensing circuit means operative to generate an output current deviating from a predetermined norm in response to variations in the output current of said power supply circuit from a predetermined value, and
 2. second circuit means operative in response to a variable bias signal to generate high-frequency pulses of variable width and substantially constant amplitude;
 2. The power supply circuit according to claim 1 wherein said first circuit means comprises:
 2. saw-tooth pulse generating means synchronized with said high-frequency oscillator means;
 3. a filtering capacitance connected between said second terminals of said first and second inductances.
 3. The power supply circuit according to claim 2 wherein said first and second inductances are inductively coupled by a common magnetic core.
 3. third circuit means which, when coupled to the variable-impedance load is operative in response to the output of said second circuit means to generate high frequency, high voltage output power when the load impedance is high, and to generate high frequency, low voltage output power when the load impedance is low; and
 3. bias circuit means coupled to said voltage-and current-sensing circuit means and operative in response to the output voltage and current received therefrom to provide said variable bias signal to said second circuit means.
 3. a series resonant circuit interconnecting the input of said first-stage transistor switch and the output of said second-stage transistor switch.
 3. a power transistor having its base and emitter connected across said secondary winding of said transformer, and having its collector connected through said second and first terminals of said autotransformer to said first circuit means; and
 3. first amplification circuit means connected to said saw-tooth pulse generating circuit and operative to amplify the output of said saw-tooth pulse generating means and said variable bias signal;
 4. resonant circuit means connected between said first and thrid terminals of said autotransformer and operative to generate a high voltage by resonating at a first high frequency in response to input power pulses from said autotransformer when said load impedance is high, and by resonating at a second high frequency in response to input power pulses from said autotransformer when said load impedance is low.
 4. threshold circuit means having a first input terminal connected to the output of said first amplification circuit means and a second input terminal connected to the output of said high-frequency oscillator means, and operative to generate output pulses of constant amplitude and of variable width corresponding to the period of time during which both of said input pulses exceed its threshold; and
 4. fourth circuit means operative to provide a variable bias signal to said second circuit means to vary the width of the output pulses of said second circuit means in response to variations in the output voltage and current from their predetermined normal levels.
 4. The power supply circuit according to claim 1 wherein said second circuit means comprises:
 5. second amplification circuit means operative to generate output pulses of predetermined polarity, constant amplitude, and variable width corresponding to the width of the output pulses of said threshold circuit means.
 5. The power supply circuit according to claim 4 wherein said high-frequency oscillator mEans comprises:
 6. The power supply circuit according to claim 5 wherein said high-frequency oscillator means is operative to close a discharge current path for said saw-tooth pulse generating means through said second transistor switch in the periods between adjacent high-frequency rectangular pulses.
 7. The power supply circuit according to claim 4 wherein said threshold circuit means comprises a NAND gate.
 8. The power supply circuit according to claim 4 wherein said second circuit means further comprises voltage regulation means.
 9. The power supply circuit according to claim 8 wherein said saw-tooth pulse generating circuit comprises:
 10. The power supply circuit according to claim 1 wherein said third circuit means comprises:
 11. The power supply circuit according to claim 1 wherein said fourth circuit means comprises: 